Hai-Ping Hu

Study on monotonicity of boundary value problems of differential equations

This article presents two new test methods to decide monotonic increasing or decreasing properties of differential equations. For simple problems, the eigenfunction test method can be applied to obtain their exact monotonicity or their loosest conditional expression, and can contribute to probes into accumulated effect of various terms in equations on their monotonicity. Secondly, the trial function test method sets relatively strict conditions for discrimination of monotonicity, but it can verify complex non-linear problems in a simple and rapid way. Therefore, these two similar test methods will help to further understand theories on monotonicity, thus making it possible to apply monotonic equations more widely to other problems.

Forced Convection in Film Condensation on a Horizontal Elliptical Tube

The aim of the present study is to investigate film condensation on an isothermal elliptical tube employing the model of Sarma et al. (1998). The study also considers the transition from laminar to turbulent film. The paper then presents analytical analysis for the local dimensionless film thickness and heat transfer characteristics for different degrees of tube eccentricity. Finally, the results developed in this study are compared with those generated by previous theoretical and experimental research. It is noted that the correlation between the two sets of data is quite satisfactory.

Turbulent Film Condensation on an Isothermal Sphere

An investigation is presented of turbulent film condensation on a sphere. It begins by considering the case of vapor flow past an isothermal sphere. The high tangential velocity of the vapor flow at the boundary layer is determined from potential flow theory. The Colburn analogy is used to define the local liquid‐vapor interfacial shear that occurs for high-velocity vapor flow across the spherical surface. The results generated for the local dimensionless film thickness and heat transfer characteristics are discussed. Finally, the results developed in the current study are compared with those generated by previous theoretical and experimental results for laminar flow. It is found that the correlation between the two sets of data is quite satisfactory for low-vapor velocity. However, at the higher vapor velocities, the rate of increase of the coefficient with velocity is greater than that associated with laminar theory. It other words, for high-vapor velocity, the onset of turbulence in the condensate causes discrepancies between the two sets of data. Note that the results of the present study may be used to estimate the heat transfer coefficient more accurately than the result of previous laminar studies.

Turbulent Film Condensation on a Horizontal Elliptical Tube

This is an investigation of turbulent film condensation on a horizontal elliptical tube. The high tangential velocity of the vapor flow at the boundary layer is determined from potential flow theory. The Colburn analogy is used to define the local liquid-vapor interfacial shear which occurs for high velocity vapor flow across an elliptical tube surface

Turbulent film condensation on a half oval body

Abstract The paper is an investigation of turbulent film condensation on a half oval body. The high tangential velocity of the vapor flow at the boundary layer is determined from potential flow theory. The Colburn analogy is used to define the local liquid–vapor interfacial shear which occurs when the high velocity vapor flows across the body surface. The paper then presents a discussion of the results obtained for the local dimensionless film thickness and heat transfer characteristics. Furthermore, the present paper discusses the influence of Froude number, sub-cooling temperature and system pressure on mean Nusselt number.

FREE CONVECTION IN TURBULENT FILM BOILING ON A VERTICAL ELLIPSOID

A theoretical investigation is performed into the heat transfer efficiency of turbulent film boiling on a vertical, isothermal ellipsoidal surface. The analyses take full account of the respective effects of the vapor temperature, the nonlinear vapor velocity, the temperature-dependent properties of the vapor, the eddy diffusivity, and the radiation emissivity. The results show that the heat transfer efficiency improves with an increasing eccentricity, radiation emissivity, temperature ratio, and Grashof number. Furthermore, it is shown that the present results are in good agreement with the theoretical and experimental findings presented in the literature.

An analysis of turbulent film condensation on an inclined tube with variable wall temperature

The present study aims to investigate turbulent film condensation on an inclined tube with variable wall temperature. The analysis proceeds under the effects of liquid–vapour interfacial shear and eddy diffusivity. In order to forecast the results more exactly, a new theory model of local film shear stress (τ/τw) is presented in the paper. The numerical calculation is obtained by using Visual C++.Net. The results show that the increase in the temperature amplitude will bring about a larger Nusselt number under high velocity vapour. Besides, the results present the optimal inclination angle of the tube in different wall temperature amplitudes.

The Two-Dimensional Heat Transfer Analysis in Arrayed Fins with the Thermal Dissipation Substrate

The aim of the present study is to investigate the two-dimensional heat transfer analysis in arrayed fins with thermal dissipation substrate. The governing equations for the fins and the substrate are expressed with Laplace equations, and the boundary conditions around the fins and substrate are Robin conditions. The present investigation first aims to provide a solution with regard to the geometry models by a series truncation method. Then the research will compare the results of the series truncation method with the point-matching method. Furthermore, the present study will also discuss the effects of dimension and Biot number of the fins on local dimensionless temperature, mean temperature, and heat transfer rate.

An Analysis of Turbulent Film Condensation on an Inclined Tube

The aim of this present study is to investigate turbulent film condensation on an isothermal inclined tube. Analyses are under the effects of liquid-vapor interfacial shear and eddy diffusivity. Results are obtained for the heat transfer coefficient over a wide range of vapor velocities. The optimal inclination angle of the tube in different length-radius ratios can be obtained in the present results. Finally, there is a comparison between the present study and those results generated by previous theoretical and experimental results. It is noted that the correlation between the two sets of data is quite satisfactory.

Surface Tension Effects in Turbulent Film Boiling on a Horizontal Elliptical Tube

DOI: 10.2514/1.30222 The present theoretical study investigates turbulent film boiling on an isothermal elliptical tube under free convection. The effects of surface tension, eccentricity, and radiation are included in the analysis. Temperature, velocity, and heat transfer characteristics are discussed. The temperature and velocity of the vapor film under the eddydiffusivitypresentthenonlineardistribution.Inaddition,underhighereccentricityvalues,theeccentricityand the surface tension have only little influence on the mean Nusselt number. Furthermore, for film boiling with higher Rayleigh values, the elliptical tube can get better heat transfer efficiencies than can a circular tube. However, when Rayleigh values are low, the eccentricity of an elliptical tube seldom influences the heat transfer.